The way Tally applies a credit note to an invoice requires two payments to be created. If you use the button provided to apply a credit note to an invoice then the payments are automatically created using a Bulk Payment.
Assuming the credit note is for £100 then a payment is added to the Credit Note for -100 (negative amount) and a payment is added to the invoice for 100 (positive amount). Because they are payments, the system insists on using a bank account (and a payment method) for the payment. As the payment totals zero then it doesn't affect the bank account balance. In fact, as the bulk payment totals zero, it doesn't even show in the list of transactions for the bank account when viewing the list or reconciling the account. So whilst it's odd/distracting that a bank account name and payment method is mentioned against the payment - you can totally ignore this as it doesn't affect your accounts in any way.